The weapon would've been 200 times as powerful as Tsar Bomba, the largest nuclear blast ever created by human hands. It was thought to be capable of destroying continents and contaminating the entire earth, so much so that no method of delivering the bomb was ever bothered with. After all, a detonation anywhere would wipe out life everywhere.

Soon after America set off its largest-ever nuclear blast on Bikini Atoll in the Pacific, one of the scientists behind the weapon's design aimed for something even bigger: a 10,000-megaton blast that would've been 670,000 times as powerful as the bomb dropped on Hiroshima, so large it would've destroyed a continent and poisoned the earth.

But even while working on the atomic bomb during World War II, Teller and a few others were urging for a much larger "super bomb" than the first atomic weapons. They believed that, while the atomic bombs were aiming for about 10-15 kilotons of power, weapons that would boom at 10-15 megatons were possible.

The Castle Bravo test was the largest nuclear blast ever created by the U.S.

(U.S. Federal Government)

He proposed linking together multiple thermonuclear devices to create larger blasts. Slight permutations on this idea led to the U.S. CASTLE Bravo test with a 15-megaton yield—the largest America ever set off, and the Tsar Bomba display by Russia—the largest nuclear blast ever created by man at 50-megatons.

But at the Castle test series in 1954, while Teller and Ulam's overall concept of thermonuclear devices was being proven over and over, the only individual bomb actually designed by Teller himself was a dud. It went off at only 110-kilotons, a tiny fraction of power compared to every other weapon tested in the series.

And Teller had a lot riding on success. The U.S. had split its nuclear efforts into two labs, adding Livermore National Laboratory to Los Alamos where the original atomic bombs had been created. Teller was one of the founders of Livermore, and his friends were helping run it. There were rumors that the government might stop funding Livermore efforts, effectively killing it.

So Teller went to the next meeting with the General Advisory Committee, where the nuclear scientists proposed new lines of effort and weapon designs, with two proposed ways forward for Livermore. He wanted the laboratory to look into tactical nuclear weapon designs on one hand, and to create a 10,000-megaton nuclear weapon on the other hand.

A 10,000 megaton weapon, by my estimation, would be powerful enough to set all of New England on fire. Or most of California. Or all of the UK and Ireland. Or all of France. Or all of Germany. Or both North and South Korea. And so on.

But that only accounts for the immediate overpressure wave and fireball. The lethal nuclear fallout would have immediately lethal levels of radiation across multiple countries, and likely would have poisoned the earth. We would show you what this looks like on NUKEMAP, but Wellerstein programmed it to "only" work with blasts up to 100 megatons, the largest bomb ever constructed. Teller's weapon would have been 100 times as powerful.

The NUKEMAP application shows the damage from a 100-megaton blast on Moscow. The orange and yellow ovals going northeast are the fallout from the blast. While this may look safe for America, Teller's proposed design would've been 100 times larger.

(NUKEMAP screenshot. Application by Alex Wellerstein)

When Teller went to the GAC with this proposal, they quickly threw cold water on it. What would be the point of such a weapon? It would be impossible to use the weapon without killing millions of civilians. Even if the bomb were dropped in the heart of the Soviet Union, it would poison vast swaths of Western Europe and potentially the U.S.

The GAC did endorse Livermore's work on tactical nuclear weapons, and Teller eventually moved on to other passions. But the weapon is theoretically possible. But hopefully, no one can assemble a team sufficiently smart enough to design and manufacture the weapon that's also stupid enough to build it.

After all, we already have nuclear arsenals large enough to destroy the world a few times over. Do we really need a single bomb that can do it?

(H/T to The Pentagon's Brain, a book by Annie Jacobson where the author first learned about Teller's proposal.)